This invention pertains to the art of radio devices and particularly to supperregenerative type radio devices.
The invention is applicable to a container for a superregenerative type radio receiver for receiving high frequency transmissions and, more particularly, to a superregenerative type radio receiver to be used in an environment, such as an automobile chassis, including nearby metallic objects. Such a receiver may be advantageously employed in conjunction with a low tire warning system as is disclosed in U.S. Pat. No. 4,237,728. However, it will be appreciated by those skilled in the art that the invention can be readily adapted for use in other environments as, for example, where similar radio devices are employed in other types of areas.
Superregenerative type radio receivers are advantageously employed in situations involving high frequency, low power transmission of radio signals, such as may be typically used in an automatic garage door opener. Most manufacturers of superregenerative receivers are especially desirous of high volume production at low cost. Typically, the entire radio receiver circuit is contained on a single circuit board and the antenna therefore comprises a printed circuit trace on the circuit board. In addition, inductors for the circuit may similarly comprise mere wire loop traces upon the circuit board.
The various forms and types of superregenerative radio receivers and containers therefore that have heretofore been suggested and employed in industry have met with varying degrees of success. It has been found that the defects present in most prior superregenerative type radio receivers are such that the devices themselves are of limited economic and practical value.
Superregenerative radio receivers suffer from the problem of being inherently unstable and inclined towards frequency shift especially when the receiver is brought into the vicinity of nearby metallic objects or objects that are capable of exerting a capacitive effect upon the circuit elements. Such effects are primarily exerted upon the circuit elements such as unshielded capacitors and inductors which may typically merely comprise wire loop traces. In addition, reflections of transmitted radio waves to a superregenerative receiver antenna, when reflected to the antenna out-of-phase from the original transmission can hamper receiver operation.
Numerous of ideas have been suggested to force frequency stability in superregenerative receivers. Many of such ideas pertain to circuit add-ons which tend to stabilize free air frequency, but fail to maintain the constant tuned frequency when near radio capacitive objects or radio wave reflective surfaces. Other methods of stabilization include encasing the entire receiver in a metal chassis with an external antenna; however, this method is still prone to the disadvantages of having out-of-phase reflections from metallic surfaces near the protruding antenna. In addition, the circuit add-ons and metal chassis containers are relatively high cost items in comparison to the receiver circuit itself.
The present invention contemplates a new and improved superregenerative type receiver which overcomes the bulk of the above referred to problems and others to provide a superregenerative receiver which is simple in design, includes a printed circuit antenna on the circuitry board, avoids costly frequency stabilizing add-ons, provides in-phase gain of reflected transmissions to the circuit antenna and provides a high degree of frequency stability in a receiver regardless of the installation environment of the receiver.